Styrofoam Cakes

I want to practice because I have time but I don't want to make cakes that I don't have anyone to give them to, such a waste. Styrofoam boards are a good option but because they're expensive can they be reused?

You certainly can. I put a thin layer of Crisco on my dummies before covering with fondant. It makes it easier to remove when I'm ready to change designs. The Crisco also helps the fondant to adhere to the dummy.